1. Field of the Invention
The present invention relates to a receiver for receiving text-based multiplex broadcasts such as FM text-based multiplex broadcasts.
2. Description of the Related Art
In Japan, for example, FM broadcasts called "FM text-based multiplex broadcast" are realized in which character information data or the like is multiplexed and transmitted together with the original audio broadcast program. Meanwhile, FM receivers for receiving these broadcasts and displaying character information on a display device, such as a liquid crystal display device (LCD), are also commercially available.
Such FM text-based multiplex broadcast, in whose development the NHK Broadcasting Technology Research Institute has played a key role, includes the capacity for mobile reception in an automobile or the like, and is called a DARC (DAta Radio Channel) method. The multiplexing standard for digital data, such as character information, is as follows: a subcarrier frequency of 76 kHz, a transmission rate of 16 kilobits per second, a modulation method of LMSK (Level-Controlled Minimum Shift Keying), and an error correction method using a (272, 190) compacted difference set cyclic code.
Program services such as character information can be classified into levels 1, 2 and 3. In all three cases, character information is displayed using a dot display. In level 1, the information is provided as character information targeted as a service for a receiver capable of displaying 15.5 characters.times.2.5 lines, including a header. In level 2, the information is provided as characters or figures targeted as a service adopting a receiver capable of displaying 15.5 characters.times.8.5 lines, including a header. Level 3 is for traffic information services provided for receivers capable of displaying detailed maps from a CD-ROM (Compact Disc Read-Only Memory) or the like, namely, navigation systems.
Level 1 program services can be utilized for news, weather forecasts, traffic information, entertainment, main supplemental programs and the like. Entertainment would include services providing fortune telling, messages from listeners, quizzes, town information and the like.
A main supplemental program provides information for supplementing a program such as the song name, performers name and telephone and fax numbers for requests when the original audio broadcast program is, for example, a music program. The main supplemental programs will be hereinafter referred to as "program information" or "program linkage".
In addition to the above services, "emergency information" may also be provided as required at the time of emergencies.
FIG. 3 shows the frame structure of an LMSK signal which is multiplexed in the FM text-based multiplex broadcast of a DARC method. One frame of this LMSK signal is comprised of 272 blocks, with each block comprising 288 bits.
One frame comprising 272 blocks is divided into 190 data packet blocks and 82 vertical parity packet blocks, with the vertical parity packet blocks being distributed and transmitted.
A 16-bit BIC (Block Identity Code) is attached to the head of each block. Four kinds of BIC are used for distinguishing each of the parity packets, and thus the heads of the frames can be discerned.
The data packet block has a 176-bit data packet following the BIC, after which a 14-bit CRC (Cyclic Redundancy Check) code is added, followed by an 82-bit horizontal parity check code. The CRC code is attached for detecting residual errors after error correction using a product code. The vertical parity packet block is provided to have a 272-bit vertical parity packet following the BIC.
Each data packet comprises a 32-bit prefix followed by a 144-bit data block, as shown in the upper portion of FIG. 4.
This prefix comprises a service identity code, a decode identity flag, an information end flag, a renewal flag, a program number, a page number, a data link code and a data packet number, as shown in the lower portion of FIG. 4.
The service identity code consists of 4 bits and is for discerning the program contents and the like. Regarding level 1, "1" is general information for sequential reception processing, "2" is general information for recording and reception processing, and "4" is for traffic information.
Sequential reception processing is a mode for the receiver starting decoding processing for displaying on receipt of the first data packet of the program data or the page data. Recording and reception processing is a mode for not starting decoding processing for displaying until all of the data for the program data or the page data are received and recorded and then error correction is carried out the CRC code for every data group.
Sequential reception processing is carried out for a program where the information must be transmitted with preparation of suitable display timing on the receiving side or for a program where the information will not be displayed in time if the decoding processing is started after the last packet of the data group is obtained.
In the prefix, the decode identity flag is one bit, and is "1" when the error correction circuit for the receiver outputs data by decoding in the horizontal direction only, and "0" when the data is output after decoding in the horizontal direction and the vertical direction.
Sequential reception processing when the decode identity flag is "0" is defined in such a manner that decoding processing for displaying each of the data packets is carried out at the time when the receiver receives the BIC at the head of the 302nd packet from receipt of the BIC at the head of the first data packets.
The information end flag is one bit and is "1" when transmission of a data group with a certain data group number is completed, and "0" when this is not the case. The renewal flag is two bits, and is incremented by one every time a data group is updated. The program number is 8 bits, and the page number is 6 bits, with the data group number being formed using both of these items.
The program number is from 0 to 255, the "main menu" being assigned to "1", the main supplement program (program information or program linkage) being assigned to "254" and emergency information being assigned to "255".
The program number is from 1 to 62, i.e., one program can have a maximum of 62 pages. One page corresponds to one to four of the data groups, with one data group comprising one or a plurality of data blocks.
The data link code is 2 bits and is used for linking each group of the divided data group. When the data is so large that the number of the data packets belonging to one data group exceeds the maximum value of the data packet number, the data group is divided into a maximum of 4 groups with different data link codes. The data group is then transmitted with the divided groups of the same group number and different data link codes being linked in the order of the code numbers 0.fwdarw.1.fwdarw.2.fwdarw.3.
The data packet number is 8 bits long, and is aligned in sequence from 0. The data packet number indicates the sequence of the data packets in one program. That is, the data packet indicates in which position the data packet is placed in one program.
Therefore, in the same program, the service identity code and the program number become the same. Or, in a plurality of data packets, if the service identity code and the program number are the same, the data packet is a packet which forms the same program.
At level 1, one page is usually displayed in the form of 15.5 characters.times.2.5 lines, but can also be displayed in the form of 15.5 characters.times.8.5 lines. Further, in this case, the character data is for displaying characters defined by JIS (Japanese Industrial Standard) code.
As described above and as shown in FIG. 5, the receiver compatible with level 1 has, for example, an LCD (liquid crystal display device) 1 having a display screen 1a capable of displaying 15.5 characters.times.2.5 lines. The 15.5 characters by 2 lines portion 1b of the lower portion of the display screen 1a is for displaying text and the 0.5 line portion 1c of the upper portion is a header text display screen.
The receiver receives a stereo composite signal and an LMSK signal, and decodes the character data from this LMSK signal to write the data in a buffer memory.
A "main menu" key is provided at the receiver and the receiver displays the main menu on the display screen 1a as a result of the manipulation of this key, in the way shown in FIG. 6A. FIG. 6A shows characters "1. PROGRAM INFORMATION" and "2. NEWS AND SPORTS" displayed as the first page of the main menu extending over a plurality of pages or the first 2.5 lines of a page of a text in an 8.5 lines display format.
Displayed in the header section are the broadcasting station name 1d which is broadcasting the FM text-based multiplex broadcast that is currently being received by this FM receiver, the service (company) name 1e of the FM text-based multiplex broadcast, and the menu name 1f.
The receiver is further provided with a "page (screen) scroll" key. By operating this key, "3. WEATHER FORECAST" and "4. TRAFFIC INFORMATION" of the next page or the next two lines of text of a page in the 8.5 line display format are displayed on the display screen 1a, as shown in FIG. 6B.
When the user decides upon the number of an item that the user wishes to see from the main menu, then the menu of the selected item is further made to be displayed. For example, when the user selects "3. WEATHER FORECAST" from within the main menu, then the contents "1. TODAY'S WEATHER 2. TOMORROW'S WEATHER" are displayed, as shown in FIG. 6C.
Further, when the user decides upon the number of an item that the user wishes to see from within the menu, then the first page of the selected item is shown. For example, when the user selects "1. TODAY'S WEATHER" from the menu, specific character information relating to the "1. TODAY'S WEATHER" is displayed, as shown in FIG. 6D.
FIGS. 6A to 6D show displays in Japanese in compliance with the JIS standard. For reference, the displays of FIGS. 6A to 6D in English are shown in FIG. 7A to 7D, respectively (in the DARC method, display and transmission in only English is not yet performed; however, there is a possibility that transmission compatible with an English display will be performed in the future).
The above describes a case in which FM text-based multiplex broadcasting provides a program of text information or the like. In the FM text-based multiplex broadcast, it is further envisioned that a paging system will be provided. Such paging system is a pay service offered to users individually who have signed a contract beforehand, and calls a user individually as a pager and provides stock prices, horse racing information, specific news, and the like.
In this paging system, as shown in FIG. 8A, each data packet is made up of a prefix of 16 bits and a data block of 160 bits. The prefix, as shown in FIG. 8B, is made up of a service identity code, a decoding identity flag, an information end flag, a renewal flag, a data group number, and a data packet number.
Data in which the service identity code and the data group number of the above elements are excluded is the same as that when a program service for the above-described character information is provided; when a paging system is to be provided, the service identity code is set at 11: paging information.
The data group number is 4 bits and indicates the data group in the paging system. In the case of the paging system, the data group is made up of one or more data blocks, as shown in FIG. 9A.
Further, the information in the case of the paging system is composed of information units called segments. Since a segment is usually smaller than a data block, as shown in FIG. 9B, one data group is formed of one or more segments, with the data group ending with a 16-bit CRC code for detecting errors of the data group. Since the length of the segment is arbitrary, when unnecessary bits occur between the end segment and the CRC code, those bits are set to "0" (null codes).
The segment, as shown in FIG. 9C, is made up of a segment header of 1 to 4 bytes and segment data of 1 or more bytes. The segment header, as shown in FIG. 9D, is made up of a segment identity code of 4 bits and segment length data formed by the remaining bits.
In this case, the segment identity code indicates the contents of the segment data, and the segment length data indicates the length of the segment data, namely, the number of bytes. The values of the segment identity codes and the contents indicated thereby are set as follows: 13: calling data, 10: alternate frequency information, 1: scramble information, and 9: common information.
When the contents of the segment data indicated by the segment identity code is calling data, the segment data, when users who have been registered beforehand are called individually or in group, is an identity code which specifies that user. Further, when information is to be sent to that user, the segment data has data relating to such information.
In the case of alternate frequency information, the segment data is alternate frequency information for paging information. In the case of scramble information, the segment data is scramble information for encryption. In the case of traffic information, the segment data is information common to all users.
When the contents of the segment data indicated by the segment identity code is calling data, the calling data (the segment data) is formed into a structure as shown in FIG. 10.
That is, the ID group identity code is 2 bytes in size and is, when the identity code which specifies the user is formed into a group, data which specifies the group. A message identity code (MID) is 2 bits in size and indicates whether or not a message (data) is attached to the identity code. The values and the contents the ID group identity code are set as follows: 0: a message is present in the identity code, 1: no message is present in the identity code, 2: undefined, and 3: undefined.
The number of calls indicates the number of users (the number of identity codes) to be called by this calling data. Following this number of calls, the identity codes of the users who are called actually are each written in the size of 3 bytes. FIG. 10 shows a case in which there are N users who are called at MID=0, and there are M users who are called at MID=1.
When MID=1, messages are sent to the M users respectively. The data which indicates the type of the contents for each message is a character type. This character type is 2 bits in size, and the values and the contents thereof are set as follows: 0: fixed-type message, 1: numeral.fixed-type message, 2: character (8-unit code system), and 3: binary data.
In such a case, when the character type is a fixed-type message, the remaining 6bytes is made to be data for selecting one of the plurality of fixed-type messages which are prepared beforehand, and no message is assumed to has been input.
When the character type is a numeral.multidot.fixed-type message, numerals and several kinds of symbols are represented by 4-bit codes, and a message is sent in 4-bit units. When the character type is a character, a message is sent mainly in characters of Kanji and the like, and when the character type is binary data, a message in binary data is sent. Further, for each character type, data indicating the data length of the message follows, as well as an actual message.
Therefore, if the following is performed, the user is able to individually receive information services. That is, a ROM in which the above-described identity code is written is provided in the FM receiver of the user. When calling data is received, the identity code contained in the calling data is compared with the identity code written in the ROM. When the result of the comparison is no match, no action is taken; however, when the comparison results in a match, a corresponding process is performed in accordance with the MID and the message.
In this way, the following services can be realized:
users are called individually PA1 messages are sent to the users individually, for example, information, such as stock prices, horse racing information, or specific news, is provided to a user who has signed a contract beforehand.
As described above, use of a paging system of an FM text-based broadcast makes it possible for a user who has signed a contract beforehand to receive information services individually.
However, in order to write an identity code in the ROM of the FM receiver, the user must bring or send that FM receiver to an information service agency having a ROM writer. Further, it is necessary for that agency to prepare a ROM writer. It is further necessary to train persons who are able to handle the ROM writer. Further, since an identity code is written in the incorporated ROM, the FM receiver must be provided with a connector for connection purposes. Thus, the number of parts of the receiver is increased, and the receiver becomes complex.